The invention relates to devices and methods for assessing the integrity of structures by measuring the response of the structures to applied excitation. More particularly, power transmission line cross-arms, vertical poles, and other wooden structures are tested while in service. The testing comprises applying a shock by physical impact, and determining the response of the subject structure to the shock. In one embodiment, instrumentation is placed or mounted temporarily on the structure, for example at one end of an elongated wood cross-arm structure. An impact is applied at a remote point, such as the opposite end, using a sensor equipped hammer to apply the shock and to trigger timing. The shock is sensed and reported to a recording device. Sensing and/or reporting can involve a wireless data signal path or a wireless excitation/response path, for example using radar. Attributes of the results correlate with structural integrity.
A lateral span of thickness or other dimensional measurement can be factored into the analysis of the response to the impact. A gamma ray source/detector pair can be used to measure opacity to radiation, which with dimensions is a measure of material density.
Preferably, a sharp impact is applied on the excitation side, using a weight coupled to an accelerometer. The accelerometer produces timing triggering signals and enables assessment of the hardness or softness of the structure at the point of impact.
An acoustic wave from the impact propagates through the structure and is detected at a remote point, such as the opposite end. The detected wave can be analyzed for propagation time, amplitude, dispersion and the like. A range of measurements taken in this manner are useful to distinguish intact cross-arms from those having damage from one cause or another.